1. Field of the Invention
The invention relates to a gear machining apparatus that causes a machining tool and a workpiece to rotate at a high speed in synchronization with each other, thereby machining a gear through cutting.
2. Description of the Related Art
Conventionally, in order to machine a gear through cutting with the use of a machine tool such as a machining center, there has been adopted, for example, a machining method described in Japanese Patent Application Publication No. 2012-51049 (JP 2012-51049 A) as a technique for efficiently machining internal teeth and external teeth. In this machining method, a machining tool such as a skiving tool having a plurality of tool blades, which is rotatable about the tool rotational axis, and a workpiece rotatable about the workpiece rotational axis that is tilted with respect to the tool rotational axis by a prescribed angle are rotated at a high speed in synchronization with each other while the machining tool is fed along the workpiece rotational axis to cut the workpiece. In this way, teeth of a gear are formed.
However, in this machining method, multiple tool blades are brought into contact with the workpiece at the same time, and thus a cutting resistance tends to be high. Thus, self-excited vibrations are likely to occur during cutting, which causes a possibility that the tooth trace accuracy of the gear will be deteriorated (the deviation of the actual tooth trace of the gear from the ideal tooth trace will increase). If the tool diameter of the machining tool is reduced, the number of the tool blades that are brought into contact with the workpiece is also reduced. However, there is a possibility that the stiffness of the machining tool will be reduced.
Therefore, JP 2012-51049 A describes a machining method in which the machining tool is moved in a feed path direction that extends along the surface of each tooth of the workpiece. In the machining method, the machining tool is moved relative to the workpiece in the feed path direction at a variable feed speed. With this machining method, because the intervals between fine machining scratches become irregular along the surface of each tooth, it is possible to reduce noise generated from the site of meshing between the machining tool and the workpiece, that is, self-excited vibrations during cutting.
In the machining method described in JP 2012-51049 A, it is necessary to vary the feed speed of the machining tool relative to the workpiece. As a result, the feed control is complicated. Thus, it is difficult to enhance the degree of accuracy of the tooth profile of the gear.